POS0318 DISTINCTION AND PROGNOSIS OF EARLY ARTHRITIS PHENOTYPES: AN ANALYSIS IN THREE EUROPEAN COHORTS
Authors: A. Sepriano, B. Van Dijk, S. Ramiro, A. Van der Helm – van Mil, B. Combe, D. Van Schaardenburg, M. De Wit, A. Kent, E. Mateus, R. B. M. Landewé
Journal: Annals of the Rheumatic Diseases (2023)

<h3>Background</h3> Patients (pts) with early arthritis (EA) may present with more or less classical inflammatory disease phenotypes. It is difficult to discern at presentation those who will evolve to a well-defined phenotype (e.g., rheumatoid arthritis; RA) from those who will remain undifferentiated or even will have non-inflammatory disease. The 2010 RA classification criteria were developed to promote early identification of RA and were validated against the external standard of 'expert diagnosis', a well-known approach that -however- may lead to circularity. <h3>Objectives</h3> Obtain a more unbiased insight into the 'Gestalt' of EA, by circumventing expert opinion, and investigating the latent phenotypes underlying EA and whether there are differences in prognosis across these phenotypes over time. <h3>Methods</h3> Three cohorts of pts with EA (Reade, ESPOIR and EAC) were analyzed separately. Clinical data were collected up to 12 (ESPOIR), 13 (Reade) or 24 (EAC) years. Hands and feet radiographs were scored, according to the Sharp van der Heijde method (SvdH) up to 10 (ESPOIR), 13 (Reade) and 14 (EAC) years. Latent class analysis was used to estimate the latent (i.e., unobserved) classes of EA. Each class was labelled by us, according to its most prominent features. Outcomes were functional disability, quantified by the health assessment questionnaire (HAQ), quality of life (QoL) quantified by the short form 36 physical (SF36 PC) and mental (SF36 MC) components (in ESPOIR) and radiographic damage (SvdH score). The association between class-membership and each outcome over time was tested in multivariable GEE models. <h3>Results</h3> In total, 390 (Reade), 798 (ESPOIR) and 1878 (EAC) pts were included. In ESPOIR, 4 latent classes could be distinguished (Figure 1); Two classes had a high likelihood of symmetrical polyarthritis. One of these, labelled as autoimmune inflammatory polyarthritis (AIPA), had a high likelihood of acute phase reactants (APR)-elevation and autoantibody (AB)-positivity, while the other (mild inflammatory polyarthritis; MIPA) had not. The third class had fewer joints involved (oligoarthritis of upper limbs; OAUL) and the fourth included pts with oligoarthritis of the lower limbs (OALL). All classes, except the latter, were also identified in Reade. In the EAC, OAUL could further be divided into autoimmune OAUL (AIOAUL) and mild-inflammatory OAUL (MIOAUL). In all cohorts, SvdH-scores were consistently worse in classes with AB and APR present (AIPA) than in those without. An example from the EAC cohort shows pts in the MIPA-class had on average 18.5 SvdH-units less than patients in the AIPA-class (Table 1). However, the mean HAQ- and SF36-scores were remarkably similar over time across all classes. The few statistically significant effect-sizes were small and of no clinical relevance. <h3>Conclusion</h3> EA pts presenting with elevated (APR and autoantibodies) markers, the phenotype most consistent with the 'classic RA-construct', develop more radiographic damage than those without these markers. However, pts with more damage do not necessarily have worse physical function or QoL (measured up to 24 years). These results may justify immediate DMARD-treatment for preventing damage for the proportion of EA-patients that present with an AIPA-phenotype, but not necessarily for all others. <h3>Acknowledgements</h3> AS and BvD contributed equally to this work. <h3>Disclosure of Interests</h3> None Declared.